Spring Cloud provides tools for developers to quickly build some of the common patterns in distributed systems (e.g. configuration management, service discovery, circuit breakers, intelligent routing, micro-proxy, control bus, one-time tokens, global locks, leadership election, distributed sessions, cluster state). Coordination of distributed systems leads to boiler plate patterns, and using Spring Cloud developers can quickly stand up services and applications that implement those patterns. They will work well in any distributed environment, including the developer’s own laptop, bare metal data centres, and managed platforms such as Cloud Foundry.

Features

Spring Cloud focuses on providing good out of box experience for typical use cases and extensibility mechanism to cover others.

Distributed/versioned configuration
Service registration and discovery
Routing
Service-to-service calls
Load balancing
Circuit Breakers
Global locks
Leadership election and cluster state
Distributed messaging

Spring Cloud Config

Spring Cloud Config provides server and client-side support for externalized configuration in a distributed system. With the Config Server you have a central place to manage external properties for applications across all environments. The concepts on both client and server map identically to the Spring Environment and PropertySource abstractions, so they fit very well with Spring applications, but can be used with any application running in any language. As an application moves through the deployment pipeline from dev to test and into production you can manage the configuration between those environments and be certain that applications have everything they need to run when they migrate. The default implementation of the server storage backend uses git so it easily supports labelled versions of configuration environments, as well as being accessible to a wide range of tooling for managing the content. It is easy to add alternative implementations and plug them in with Spring configuration.

Quick Start

Start the server:

$ cd spring-cloud-config-server
$ mvn spring-boot:run

The server is a Spring Boot application so you can build the jar file and run that (java -jar …) or pull it down from a Maven repository. Then try it out as a client:

$ curl localhost:8888/foo/development
{"name":"development","label":"master","propertySources":[
  {"name":"https://github.com/scratches/config-repo/foo-development.properties","source":{"bar":"spam"}},
  {"name":"https://github.com/scratches/config-repo/foo.properties","source":{"foo":"bar"}}
]}

The default strategy for locating property sources is to clone a git repository (at "spring.platform.config.server.uri") and use it to initialize a mini SpringApplication. The mini-application’s Environment is used to enumerate property sources and publish them via a JSON endpoint. The service has resources in the form:

/{application}/{profile}[/{label}]

where the "application" is injected as the "spring.config.name" in the SpringApplication (i.e. what is normally "application" in a regular Spring Boot app), "profile" is an active profile (or comma-separated list of properties), and "label" is an optional git label (defaults to "master").

Client Side Usage

To use these features in an application, just build it as a Spring Boot application that depends on spring-cloud-config-client (e.g. see the test cases for the config-client, or the sample app). When it runs it will pick up the external configuration from the default local config server on port 8888 if it is running. To modify the startup behaviour you can change the location of the config server using bootstrap.properties (like application.properties but for the bootstrap phase of an application context), e.g.

spring.platform.config.uri: http://myconfigserver.com

The bootstrap properties will show up in the /env endpoint as a high-priority property source, e.g.

$ curl localhost:8080/env
{
  "profiles":[],
  "configService:https://github.com/scratches/config-repo/bar.properties":{"foo":"bar"},
  "servletContextInitParams":{},
  "systemProperties":{...},
  ...
}

(a property source called "configService:<URL of remote repository>/<file name>" contains the property "foo" with value "bar" and is highest priority).

Sample Application

There is a sample application here. It is a Spring Boot application so you can run it using the usual mechanisms (for instance "mvn spring-boot:run"). When it runs it will look for the config server on "http://localhost:8888" by default, so you could run the server as well to see it all working together.

The sample has a test case where the config server is also started in the same JVM (with a different port), and the test asserts that an environment property from the git configuration repo is present. To change the location of the config server just set "spring.platform.config.uri" in "bootstrap.yml" (or via System properties etc.).

The test case has a main() method that runs the server in the same way (watch the logs for its port), so you can run the whole system in one process and play with it (e.g. right click on the main in your IDE and run it). The main() method uses target/config for the working directory of the git repository, so you can make local changes there and see them reflected in the running app.

$ curl localhost:8080/env/foo
bar
$ vi target/config/bar.properties
.. change value of "foo", optionally commit
$ curl localhost:8080/refresh
["foo"]
$ curl localhost:8080/env/foo
baz

The refresh endpoint reports that the "foo" property changed.

Spring Cloud Netflix

This project provides Netflix OSS integrations for Spring Boot apps through autoconfiguration and binding to the Spring Environment and other Spring programming model idioms. With a few simple annotations you can quickly enable and configure the common patterns inside your application and build large distributed systems with battle-tested Netflix components. The patterns provided include Service Discovery (Eureka), Circuit Breaker (Hystrix), Intelligent Routing (Zuul) and Client Side Load Balancing (Ribbon).

Service Discovery: Eureka Clients

Example eureka client:

@Configuration
@ComponentScan
@EnableAutoConfiguration
@EnableEurekaClient
@RestController
public class Application {

	@RequestMapping("/")
	public String home() {
		return "Hello world";
	}

	public static void main(String[] args) {
		new SpringApplicationBuilder(Application.class).web(true).run(args);
	}

}

(i.e. utterly normal Spring Boot app). Configuration is required to locate the Eureka server. Example:

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8080/v2/
      default.defaultZone: http://localhost:8080/v2/

The default application name, virtual host and non-secure port are taken from the Environment is ${spring.application.name}, ${spring.application.name}.mydomain.net and ${server.port} respectively.

Service Discovery: Eureka Server

Example eureka server:

@Configuration
@EnableAutoConfiguration
@EnableEurekaServer
public class Application {

	public static void main(String[] args) {
		new SpringApplicationBuilder(Application.class).web(true).run(args);
	}

}

The server has a home page with a UI, and HTTP API endpoints per the normal Eureka functionality under /v2/*.

Eureka (apache → tomcat) see flux capacitor and google group discussion.

Circuit Breaker: Hystrix Clients

Circuit Breaker: Hystrix Dashboard

Turbine

Declarative REST Client: Feign

Client Side Load Balancer: Ribbon

External Configuration: Archaius

Router and Filter: Zuul

Spring Cloud Cluster

Spring Cloud Cluster offers a set of primitives for building "cluster" features into a distributed system. Example are leadership election, consistent storage of cluster state, global locks and one-time tokens.

Spring Platform Bus

Spring Cloud Bus links nodes of a distributed system with a lightweight message broker. This can then be used to broadcast state changes (e.g. configuration changes) or other management instructions. The only implementation currently is with an AMQP broker as the transport, but the same basic feature set (and some more depending on the transport) is on the roadmap for other transports.

Quick Start

Spring Cloud for Cloud Foundry

Integration between Cloud Foundry and Spring Cloud.

Service Broker Example

Example script to deploy and regis#ter a broker:

DOMAIN=mydomain.net
cf push app -p target/*.jar --no-start
cf env app | grep SPRING_PROFILES_ACTIVE || cf set-env app SPRING_PROFILES_ACTIVE cloud
cf env app | grep APPLICATION_DOMAIN || cf set-env app APPLICATION_DOMAIN ${DOMAIN}

cf services | grep configserver && cf bind app configserver

cf restart app
cf create-service-broker app user secure http://app.${DOMAIN}

for f in `cf curl /v2/service_plans | grep '\"guid' | sed -e 's/.*: "//' -e 's/".*//'`; do
    cf curl v2/service_plans/$f -X PUT -d '{"public":true}'
done

cf create-service app free appi

At which point you have a service called "app" and a service instance called "appi":

$ cf marketplace
OK

service        plans   description
app            free    Singleton service app
$ cf services
Getting services in org default / space development as admin...
OK

name           service        plan   bound apps
appi           app            free

Your application can define a configuration property application.domain (defaults to "cfapps.io") which will be used to construct the credentials for any app that binds to your service. Or it can define the URI directly using cloudfoundry.service.definition.metadata.uri.

You can change some other basic metadata by setting config properties:

cloudfoundry.service.definition.* is bound to a ServiceDefinition (defined in spring-boot-cf-service-broker) which has optional setters for plans and metadata.
cloudfoundry.service.broker.* is bound to an internal bean. It has optional setters for "name" (the service name), "description" (user friendly description) and "prefix" (used to create a unique id from the name).

An app which binds to your service will get credentials that contain a "uri" property linking to your service. A Spring Boot app can bind to that through the vcap.services.[service].credentials.uri environment property.

If your service also has a Eureka core dependency, and you can expose it as a Eureka service, then any service which registers with Eureka will also become a Cloud Foundry service.